Quartz vein emplacement mechanisms at the E26 porphyry Cu-Au deposit, New South Wales

Harris, Anthony C. and Holcombe, Rodney J. (2014) Quartz vein emplacement mechanisms at the E26 porphyry Cu-Au deposit, New South Wales. Economic Geology, 109 4: 1035-1050. doi:10.2113/econgeo.109.4.1035


Author Harris, Anthony C.
Holcombe, Rodney J.
Title Quartz vein emplacement mechanisms at the E26 porphyry Cu-Au deposit, New South Wales
Journal name Economic Geology   Check publisher's open access policy
ISSN 0361-0128
1554-0774
Publication date 2014-06
Year available 2014
Sub-type Article (original research)
DOI 10.2113/econgeo.109.4.1035
Open Access Status
Volume 109
Issue 4
Start page 1035
End page 1050
Total pages 16
Place of publication Littleton, CO, United States
Publisher Society of Economic Geologists
Collection year 2015
Language eng
Subject 1906 Geochemistry and Petrology
1908 Geophysics
1905 Visual Arts and Crafts
1907 Geology
Abstract Porphyry Cu-Au-Mo deposits are characterized by numerous fracturing events. Brittle fracture of mineralized intrusions and the surrounding host rocks is a consequence of hydraulic breakage caused by the interplay of the changing physiochemical properties of magmatic fluids and/or the local tectonic regime. We have mapped more than 1,400 quartz-sulfide vein sets at the Ordovician Endeavour 26 North (E26) deposit, central New South Wales, in order to constrain the processes influencing fracture development around small (∼200 m) porphyritic intrusions. Veins from intermediate levels in the E26 deposit define complicated patterns within 10 m of the porphyritic intrusions, whereas more systematic patterns occur up to 50 m from the intrusive contact. The outer parts of the ore deposit are characterized by quartz veins with orientations of ∼340° and subordinate orthogonal sets of bisecting veins at ∼240° and ∼290°. The data show a broad range of vein orientations that define a conical distribution around a vertical axis. There is a rare subset of near-horizontal veins that formed early relative to the main stage of ore-bearing vein emplacement. Many quartz veins exhibit fault displacements (at both micro- and macroscopic scales) and fabrics (including serrate fractures, slickenlines, and asymmetric fiber trails). The distribution of veins suggests that the dominant fracture array developed perpendicular to the direction of bulk finite extension, but significant vein dilation also occurred in orientations with a component of shear strain. We propose a physical model that combines intrusion-driven hydraulic fracturing into a preexisting fracture mesh to help explain the observed vein patterns and to better link fracture development and vein emplacement. Hydraulically driven deformation was important locally at E26, contributing to the formation of the irregular fracture stockwork immediately adjacent to the small intrusive bodies. The more predictable vein patterns that occur away from the porphyritic intrusions require part of the hydraulically driven extension to have reactivated the existing fracture mesh. Parts of this more systematic geometry, including the occurrence of flat veins, are probably related to the emplacement of larger (10-km diameter) magma bodies adjacent to E26, with doming causing the subordinate fracture arrays, including the gross conical distribution. Fluctuating fluid pressures, combined with hydraulically driven extension, caused dilation of preexisting and synmineralization fractures and superposition of veins with similar orientations. Vein patterns suggest that the regional stress state that existed prior to or synchronously with porphyry ore deposit formation strongly influenced vein orientation to within tens of meters away from the mineralizing intrusions. Fractures that localized ore in the E26 porphyry deposit developed in response to the infiltration of fluid batches, including magma and magmatic-hydrothermal fluids, into a regional deformation environment.
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Earth Sciences Publications
Official 2015 Collection
 
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